Superheterodyne radio receivers for accurately tuning to the frequency of a received radio signal are well known. As those skilled in the art will appreciate, superheterodyne radio receivers eliminate the need for multiple stages of frequency filtering in order to accurately tune a radio receiver to the desired frequency. This not only enhances tuning accuracy, but also eliminates many stages of variable band-pass filtering (tuning) and the need to precisely align such filters.
In a superheterodyne radio receiver, the received radio signal is mixed with the output of a local oscillator (LO), so as to form an intermediate frequency (IF).
Such mixing results in the formation of sum and difference frequencies according to well known principles. Typically, the difference frequency becomes the intermediate frequency (IF), which is then processed further, as desired.
Similarly, a microwave mixer receives a radio frequency (RF) signal and mixes it with the output from a local oscillator (LO) to produce an intermediate frequency (IF) signal.
Because of the short wavelength of microwaves, a microwave mixer may easily be formed upon monolithic integrated circuit chip. Microwave mixers are utilized whenever it is desirable to convert the comparatively higher frequency microwave signal to a lower frequency signal in applications such as satellite communications receivers, direct broadcasting satellite receivers, up and down converters, electronic warfare systems, etc.
Of course, in any such radio frequency system, it is highly desirable to match electrical impedances. Thus, it is desirable to match the impedance of the incoming radio frequency (RF) signal to that of the mixer, as well as to match the signal from the local oscillator (LO) thereto.
It is known to use baluns to achieve impedance matching between the mixer and the incoming radio frequency (RF) signal as well as the signal from the local oscillator (LO). However, such contemporary baluns as the classical Marchand parallel-line balun utilize parallel, generally straight microstrips to effect inductive impedance matching. As those skilled in the art will appreciate, such generally straight microstrips are not formed in a real estate efficient manner. The reason for using a balun structure is to transfer RF energy from an unbalanced structure to a balanced structure, e.g., a diode ring quad, in the case of a mixer.
Because of the very short wavelength of microwave electromagnetic radiation, such straight baluns have not been thought to occupy excessive integrated circuit surface area in the past. However, as integrated circuit fabrication techniques continue to improve, line widths and component sizes grow ever smaller, such that the physical dimensions of such contemporary straight baluns come excessive by comparison.
As such, it is desirable to provide a more compact impedance matching device or balun, wherein the surface area required therefor is substantially reduced as compared to contemporary straight line baluns.